Link-State Routing Can Achieve Optimal Traffic Engineering

This paper settles a long-standing question with a positive answer: optimal traffic engineering can be realized using just link-state routing protocols. In conventional link-state protocols like OSPF and IS-IS, routers compute shortest paths based on link weights, splitting traffic evenly when multiple shortest paths exist. Unfortunately, in these particular cases of link-state protocols, computing the optimal link weights for a given traffic matrix is an NP-hard problem. Even the best setting of the weights can lead to traffic loads that deviate significantly from the ideal distribution of the traffic. In this work, we show that splitting traffic over multiple paths as an exponential function of path length can achieve optimal traffic engineering. We also present a polynomial-time algorithm for computing the optimal link weights, which in practice is also much more efficient than the local-search heuristics used today. In addition, we show how to apply the algorithm to robust traffic engineering, where one set of link weights must perform well for multiple traffic matrices or failure scenarios. These results are based on our new Network Entropy Maximization framework for routingprotocol design, which parallels the role of Network Utility Maximization for congestion control.